The present invention, in some embodiments thereof, relates to an energy conversion system and, more particularly, but not exclusively, to a conversion system which upconverts energy from longer wavelengths to shorter wavelength.
Typical materials, when heated emit energy at wavelengths distributed in a manner dependent on their emissivity. An ideal material will emit radiation, when heated, at wavelengths corresponding to those of a black body. This is known as black body radiation.
Typical energy conversion systems convert energy from short wavelengths to long waves, for example, in fluorescence or in laser radiation by optical stimulation.
Since the discovery of laser action decades ago, it has been realized in diverse systems and mechanisms. These include optically, electrically, chemically, and thermally pumped lasers. A general principle to all known lasers is the need for high energy pump excitation, above the lasing photon energy. In the thermodynamic formalism, the above principle describes work that can be obtained by the excitation's chemical potential.
Apparently, all existing lasers use pump excitation quanta (electron, photon, etc.), with energy above the energy-gap of the lasing media. This is because lasing necessitates population inversion between the higher and the lower energy-gap states, which is gained by the preferred energy transfer from the pump to the higher energy state. This, by Fermi's golden role, occurs if the pump excitations have energy above the band-gap.
To understand the broad picture of pump mechanism, pump action may be related to work performed by a thermodynamic system. Here each photon's potential energy is defined by its chemical potential, μ. In this view, the conventional absorption of a pump photon followed by photoluminescence of a red shifted photon, while releasing heat to the environment is an “optical heat pump” action. The work of generating a single emitted photon is achieved by reducing the chemical potential of a single pump photon, accompanied by the extraction of heat.
In the complete thermodynamic perspective, the amount of work a system can produce is limited by its Gibbs free energy, G:G=[P·V+T·S+Σμ·N]where P is the pressure, V is volume, T is temperature, S is the entropy, μ is the chemical potential and N is the number of particles (photons). In most optical systems P and V are constant, so change in [P·V] can be excluded. An exceptional phenomenon is sonoluminescence, where UV emission is generated as sound is converted to light through a drastic change in PV. The chemical potential term, Σμ·N, relates to all known laser pump mechanisms and also to energy conversion in nonlinear processes such as second harmonic generation, where the number of photons compensates for the photon's low individual chemical potential. Using such conventional mechanisms to generate ten-fold parametric up-conversion results in a negligible efficiency.
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The disclosures of all references mentioned above and throughout the present specification, as well as the disclosures of all references mentioned in those references, are hereby incorporated herein by reference.